The first objective of this proposal is to define the mechanisms mediating the accumulation of aminoglycosides by proximal tubular epithelium. Renal clearances, free flow micropuncture, microinjection, in vivo tubular perfusion and in vitro (isolated tubule) perfusion techniques will be utilized to determine (1) the ultrafilterability of three tritium-labeled aminoglycosides (gentamicin, netilmicin and tobramycin), (2) the segmental tubular transport of these agents, (3) the role of pinocytosis in the apical membrane transport of these agents, and (4) the contribution of basolateral membrane transport to the cellular accumulation of these agents. The second objective of this proposal is to elucidate the interaction of these agents with intracellular metabolic processes that underlie the clinical expression of toxicity. Our recent observation that gentamicin induces a phospholipidosis in renal proximal tubular cells and that it stimulates the uptake of free fatty acid by renal cortical cells suggest that the pathogenesis of aminoglycoside nephrotoxicity is linked to an alteration in lipid metabolism. To test this hypothesis we will determine (1) the effects of gentamicin, netilmicin and tobramycin on the lipid content (neutral and phospholipids) of renal cortex as a function of dose and duration of drug therapy, (2) whether these agents induce a generalized or specific lipidosis, (3)the correlation between the lipidosis and the nephrotoxic potential of these agents, (4) the effects of these agents on lipid synthesis in vitro (renal cortical slices) and in vivo using radiolabel techniques, (5) the effects of these agents on free fatty acid metabolism by renal cortical slices.